There has been a trend in recent years to build a household or suburban network by using the IEEE1394 serial bus as a means of transferring video or picture data for digital household electric appliances.
While devices complying with the IEEE1394 bus are connected by wires such as cables, wiring of the cables is now a big problem as a result of the increase in the number of devices that can be connected. Accordingly, there is a growing demand for the capability to transfer, by radio, multimedia data with the same performance as that obtainable by the IEEE1394 bus (see Japanese Patent Application Laid-Open (Kokai) No. 11-355279, for example).
FIG. 14 shows a wireless configuration of the IEEE1394 serial bus. As shown, a radio bus system 21 is made up of a plurality of terminals 23a, 23b, 23c, . . . , and a hub station 22 that controls the terminals.
The hub station 22 controls the radio bus system 21 while exchanging control information with the terminals 23a, 23b, 23c, . . . which the hub station is responsible for in the radio bus system 21, so that data can be transmitted and received among the terminals.
FIG. 15 shows a block diagram of the terminal and the hub station in a radio bus system according to the prior art, schematically showing an example of the configuration of the terminal and the hub station for conducting radio communication in the radio bus system 21. The following description is based on the assumption that the terminal and the hub station according to the present embodiment have an identical configuration and use the OFDM (orthogonal frequency division multiplex) system.
The OFDM system is a multicarrier transmission system in which transfer data is modulated on a plurality of carrier waves (to be hereafter referred to as subcarriers) and then transmitted. Since this multiplexing system is effective in preventing influences on a delay wave, it has been increasingly adopted for radio communication purposes in recent years.
In FIG. 15, the terminal or hub station comprises a transmitter and a receiver.
The transmitter will be hereafter described. Data to be transmitted is input to an input terminal 1. A scrambler 2 carries out a scrambling process whereby the energy of transmission data is spread.
A Pre-IFFT processing circuit 4 performs an error correcting coding process, an interleaving process for improving error correcting performance, and a mapping process for performing multilevel modulation such as QPSK, 16QAM and 64QAM. A quantity of data necessary for the subsequent input to the IFFT circuit 5 is accumulated by a serial/parallel (S/P) converter.
The IFFT (inverse fast Fourier transform) circuit 5 provides subcarrier modulation to the transmission data. Data output from the IFFT circuit 5 is multiplied with a reception signal in an orthogonal demodulator 12 on the receiver end and then input to a preamble attachment circuit 6 for attaching a particular series (to be hereafter referred to as a preamble) which is used for the reproduction of the carrier.
The preamble is stored in a memory 3 in advance. The preamble attachment circuit 6 attaches the preamble output from the memory 3 to the head of the output of the IFFT circuit 5, before the output is fed to an orthogonal modulator 7. The orthogonal modulator 7 converts the output into an IF signal by using the carrier generated by a carrier generating circuit 8, and outputs the IF signal via an output terminal 9.
Next, the receiver will be described. The IF signal is input to an input terminal 11. An orthogonal demodulator 12 multiplies the input signal with a complex carrier which is output by a carrier reproduction circuit 13 to thereby convert the IF signal into a base band signal and outputs it to a synchronizing circuit 14.
FIG. 16 shows a block diagram of the synchronizing circuit 14. As shown, an input signal 32 is initially input to a preamble detection circuit 31. In the preamble detection circuit 31, correlation with a preamble signal 33 which is output from the memory 18 on the receiver end and which is identical to the one on the transmitter end is determined in a correlator 34. The result of correlation is judged in a decision unit 35 to detect the preamble portion.
If detected, the preamble portion is input to a frequency error detection circuit 36 and a phase error detection circuit 37, from which a frequency error signal 38 and a phase error signal 39 are derived. These results are sent to the carrier reproduction circuit 13 and are reflected in the orthogonal demodulator 12.
In an FFT (fast Fourier transform) circuit 15, the base band signal is subcarrier-demodulated. The resultant output is fed to a post-FFT processing circuit 16, where a parallel-serial (P/S) conversion processing, a demapping process for carrying out multilevel demodulation processes, a deinterleaving process, and an error correcting decoding process are performed.
Finally, the original data is reproduced by a descrambler 17, which corresponds to the scrambler 2 on the transmitter end, and is output to an output terminal 19.
Since the IEEE1394 serial bus generally had a wired configuration, there has been no need to validate the authenticity of a cable-connected terminal.
However, when the IEEE1394 bus is to be configured by radio, there are chances that a terminal participates against the expectation of the users of the radio bus system, or that a user participates in the radio bus system by mistake.
In order to prevent these problems, a procedure known as authentication must be provided whereby a terminal wishing to participate in the radio bus system notifies the hub station of a request for participation so that the hub station can authenticate the terminal based on some kind of information.
For authentication, the information must be shared between the terminal and the hub station in advance. Specifically, the terminal to be connected to the radio bus system must register in advance its information to the hub station which controls the radio bus system. If security is a priority, the exchange of information in this registration procedure should preferably be carried out via a separate route from the radio route on which data communication takes place, such as a cable or a floppy disc.
However, to register via a separate route from radio requires additional components and this directly results in increased costs. Furthermore, if radio is employed, secrecy at the time of registration must be ensured. The possibility of unauthorized use arises when, in the case of FIG. 14, for example, a terminal transmits its terminal information to the hub station for registration purposes because the other terminals could eavesdrop on the transmitted radio data even if they did not have the intention of doing so.
In view of these problems of the prior art, it is an object of the present invention to provide a radio bus system, a radio communication apparatus and a registration communication method in which a minimum level of secrecy can be ensured even when radio is employed in the procedure for registering authentication information.